The present invention relates to the determining of the wavelength dependent characteristics of an optical component.
Different requirements have to be met for measuring optical components, generally depending on the type of component and its spectral bandwidth. A pump coupler at the input of an optical amplifier, for example, may have a spectral bandwidth of 50 nm or more, whereas a Wavelength-Division-Multiplexing (WDM) de-multiplexer may have a spectral bandwidth of only 0.2 nm for each of its channels. In particular modem optical devices, such as WM or Dense-WDM (DWDM) devices, may provide one input and multiple outputs where each output has a different wavelength passband characteristics. A measurement of such a device often demands several thousand points per output to achieve the required characteristic, with one powermeter per output which have to obtain the measurement points synchronously.
Known measurement setups (cf. e.g. in xe2x80x9cFiber optic test and measurementxe2x80x9d by Dennis Derickson ISBN 0-13-534330-5, pages 358-382) for characterizing wavelength dependent optical components are normally based on a tunable laser source in combination with a wavelength meter, a tracking filter and an optical power meter (loc. cit. page 360) and connected via standard interfaces (e.g. HPIB). Instead of using a tunable laser source, a broadband light source can be applied in combination with an optical spectrum analyzer (loc cit. page 368f), however, with a limited resolution bandwidth (approximately 0.1 . . . 0.05 nm) in contrast to the tunable laser sources (approximately 10xe2x88x926 nm).
EP-A-453 176 discloses an optical fault finder which optimizes the pulse width of the test signal which is transmitted through an optical fiber. The fault finder is an optical time domain reflectometer (OTDR) having a laser source for providing a stimulus signal and a response unit for receiving a response on the stimulus signal. Both, the laser source and the response unit are controllable by a micro-processor.
EP-A-548 935 discloses an apparatus for measuring the effective refractive index in optical fibers. The apparatus comprises a tunable laser source for providing a stimulus signal to the optical component and a receiver for receiving a response of the optical component on the stimulus signal. A control unit is coupled to the tunable laser source and the receiver for controlling the functioning thereof.
U.S. Pat. No. 5,644,417 discloses an automated system for measuring transmitter data dependent jitter of electro-optic modules. The system comprises a laser source, a receiver for receiving responses on the laser signals, and a PC for controlling the system.
U.S. Pat. No. 4,664,522 discloses an optical waveguide spectrum analyzer receiving light from an external source diffracting at a grating to a pair of detectors. Data from the detectors is processed and analyzed by a computer.
Disadvantageous in either one of the known measurement setups is that those often highly complex and expensive setups are generally limited in either measurement speed, or accuracy, or even in both, and are thus not applicable or sufficient for characterizing modem optical components.
It is an object of the invention to provide an improved measuring setup for characterizing wavelength dependent optical components.
This is solved by an optical component tester and a corresponding method for determining the wavelength dependent characteristics of an optical component according to the independent claims. Further advantageous embodiments can be found in the dependent claims.
The invention provides a separation of operations within the tester into timing critical and timing non-critical operations, thus improving the processing speed and the timing behavior. This is accomplished by a specific signal processor responsible for processing all timing critical operations within the tester.
The optical component tester according to the invention provides a less complex and less expensive measuring setup in comparison to those offering the same or similar measurement speed and or accuracy. Further more, the optical component tester according to the invention allows to provide an increased performance by offering a higher measurement speed and/or accuracy for characterizing modem optical components due to an improved matching of the functional units and the central controlling by the control unit. As well the setup and modifications of the tester as the processing and emission of triggering signals can be centrally handled by the control unit.
The invention further allows to provide the optical component tester as a turnkey solution with a xe2x80x9cswitch on ready to goxe2x80x9d mode in comparison to the costly adjustment of individual components. Firmware and user interface can be adjusted to the respective application needs (usability). Additionally, the optical component tester allows to be integrated in one box providing an economic solution in terms of space and price.
The triggering of the functional units within the optical component tester and/or external devices can be accomplished by means of a flexible a trigger unit, which is preferably software controlled.
In preferred embodiments, the optical component tester comprises a wavemeter and/or an attenuator as functional units. By coupling an output of the tunable laser source directly to an input of the wavemeter and/or to an input of the attenuator, an output of the attenuator provides an improved external output for applying the stimulus signal to the optical component. An increased optical output power at the output and, in most cases, to a better performance of the laser stimulus can thus be achieved due to an increased power flatness versus wavelength with respect to a measuring setup comprising individual components as known in the art.
The tunable laser source is preferably embodied as a low noise tunable laser source as disclosed in the European Patent Application No. 97121649.4 by the, same applicant. Further more, the wavemeter is preferably embodied as a wavemeter disclosed in the European Patent Application No. 97107247.5 by the same applicart, enabling fast stimulus response measurements with wavelength resolution  less than 0.05 nm in combination with a high dynamic.
Further improvements can be achieved by loading (pre)calibration and/or setup data to the control unit, thus avoiding lengthy calibrations of the functional units, whereby the data is preferably stored and fetched on demand.
A stimulus and/or response wavelength sweep is preferably performed either in a linear wavelength mode by applying the wavemeter to ensure a linear wavelength tuning of the tunable laser source, or in a constant velocity mode by moving the tunable laser source from a first to a second wavelength, whereby the wavemeter measures the wavelength at each measuring point The latter mode is faster because there is no wavelength correction loop between the tunable laser source and the wavemeter needed.
It is clear that the tunable laser source can also be used as a source only independently of the response units.